Optimizing production of human foods is a goal of the food industry since it results in lower production costs and lower cost to the consumer. Accordingly, given the commercial importance of milk products, many methods have been proposed in the art for enhancing milk production by cows. Such methods include, for example, the use of food supplements, breeding programs, drugs, hormones and various food combinations.
One particular means of enhancing milk production by cows which has received fairly recent attention comprises the administration of fatty acids or derivatives thereof, in particular, salts and triglycerides to cows.
For example, U.S. Pat. No. 4,388,327 to Cummins teaches the administration of free fatty acids, specifically gamma-methylmercapto-alpha-hydroxybutyric acid, or its oligomers, to cows as a means for enhancing milk production.
However, fatty acids and, in particular, unsaturated fatty acids, are known to sometimes cause deleterious effects on the cow's ruminant digestive system and digestion. This is believed to be caused by their exerting toxic effects on microbia contained in the rumen which are involved in digestion. Thus, as a means for avoiding this problem, fatty acids have been administered as "rumen inert" forms. These forms include, in particular, salts, including calcium and magnesium salts of fatty acids and cross-linked protein encapsulates containing fatty acids or triglycerides. In this regard, Palmquist et al. (U.S. Pat. No. 4,642,317) teaches the administration of calcium salts of fatty acids containing at least 10 carbon atoms to ruminants as a means for increasing milk production.
As noted, it is known in the art to administer triglycerides of fatty acids to increase milk production in cows. For example, U.S. Pat. No. 4,919,940 issued to Wellons teaches a process for administering triglycerides containing fatty acids with at least 10 carbon atoms in order to enhance milk production.
It is also known in the art to administer fatty acids to increase fat content of milk. For example, U.S. Pat. No. 3,458,625 issued to Ensor et al teaches feeding lactating dairy cows unsaturated fatty acids having 14 to 24 carbon atoms resulting in increased milk production and increased fat content in the milk.
Additionally, U.S. Pat. No. 5,004,728 issued to Chalupa et al. teaches feeding lactating ruminants somatotropin in combination with long chain fatty acids or salts thereof with resulting increased milk production and increased fat content in the milk.
While it may be desirable in some instances to increase the fat content of milk, e.g., if the milk is to be used in the preparation of butter, or other high fat containing milk products it is also desirable to provide methods for the reduction of fat content of milk. This is desirable given the recent consumer demand for low fat milks and other low fat dairy products and the fact that many consumers are on low fat and low cholesterol diets. Because of the natural association of cholesterol with fat in the milk, reducing milk fat will also reduce cholesterol in milk. This is further desirable, since while milk supplies are barely adequate to meet consumer demands, butter (a typical product resulting from milk fat) is the only milk derived commodity which is in surplus and is being stored by the government. Thus, there is not much current market incentive to produce high fat milk products, but rather the current and future incentive is the production of low fat milk. Thus, a safe and inexpensive method which results in production of a natural low fat milk would be highly desirable.
It is known in the art that high levels of grain feeding can lead to milk fat depression in lactating dairy cows and that this depression can be as much as 30 to 40%. Moreover, theories have been advanced as to why high grain diets can result in milk fat depression in lactating cows. These theories include: 1) deficiency of acetate and/or butyrate which is involved in fat synthesis, 2) inhibition of fat synthesis by glucose precursors such as propionate, 3) insulin inhibition caused by propionate or glucose, and 4) deficiency of vitamin B.sub.12 and other factors which affect liver, mammary and adipose tissue metabolism. However, despite the different theories which have been advanced, dairy scientists are still unaware of the exact mechanism by which a high grain diet reduces milk fat concentrations in lactating cows.
Literature data (Palmquist and Jenkins, J. Dairy Science, vol. 63, 1980) shows that unsaturated vegetable fat that is protected from rumen degradation can increase milk fat percent while unprotected vegetable fat or hydrogenated vegetable fat can depress milk fat percent. Rumen microorganisms cause a marked biohydrogenation of unsaturated long chain fatty acids, and this process results in production of trans-octadecenoic acids.
In this regard there have been disclosed in the art various studies correlating milk fat content and relative cis or trans-fatty acid content and distribution in cow's milk. However, none of these studies have established a causative role between the amount and/or type of isomers of fatty acids ingested by cows and resulting milk fat concentrations. Essentially, these studies have merely measured milk fat levels and correlated these levels to the amount and distribution of different fatty acids contained in the milk. Such studies are of course not sufficient to establish any causal relationship between milk fat levels and the ingestion of cis or trans-fatty acids.
For example, Wonsil et al. in Abstract No. 5427 in FASEB, abstracted in 1991, teach feeding experiments wherein cows were fed a control diet of supplemental fat, or a diet containing 3% partially hydrogenated fatty acids (46% C.sub.16:0, 31% C.sub.18:0, 15% C.sub.18:1), 1.5% fish oil plus 1.5% stearic acid, or 1.5% soybean oil plus 1.5% partially hydrogenated soybean oil. They observed that the amount of trans 18:1 fatty acids increased when fish oil and soybean oil were fed, and that there was a negative correlation between trans C.sub.18:1 fatty acids and milk fat percent. However, they recognized no causal relationship between the ingestion of trans-fatty acids and milk fat percent.
A study by Rindsig and Schultz published in Journal of Dairy Science, 1980, (57:1459), disclosed experiments wherein lactating Holstein cows were either fed a control diet ration, or the control diet ration in combination with safflower oil or elaidic acid (a trans-fatty acid). They in fact, disclosed that the abomasal infusion of a trans-fatty acid, specifically trans-9-octadecenoic acid failed to depress milk fat percentages. They further noted that there was no discrimination between any particular fatty acid isomer and this reflected an equal susceptibility to lipoprotein lipase of triglycerides containing cis or trans octadecenoic acids. Thus, they also disclosed no causal relationship concerning trans-fatty acid administration to cows and resulting milk fat concentrations.
In a related study by Selner and Schultz published in Journal of Dairy Science, 1980 (63: 1253), the co-authors disclose the effect of feeding safflower oil or elaidic acid to lactating cows. They also attempted to establish a causal relationship between trans-fatty acid administration (trans-9-octadecenoic acid) and milk fat levels. They, however, disclosed that this trans-fatty acid did not depress milk fat percentages. Hence, they also found no causal relationship between ingestion of trans-fatty acids and resulting milk fat concentrations.
Finally, in a paper by Banks et at. published in Journal of Dairy Research, 1984, (51:387), the authors disclosed the results of feeding experiments relating to different forms of dietary fatty acids and milk fat concentrations and milk yields. In this study cows were fed either a control diet, or saturated fatty acids in three forms, free fatty acids, unprotected triglycerides, or protected triglycerides (triglycerides encapsulated in a cross-linked protein matrix). The authors disclosed that the control diet and the diet containing the free fatty acids produced very little trans-fatty acid isomers in the milk fat, but that the proportions of trans 18:1 fatty acids increased with the diet containing free and protected hydrogenated fatty acids. They further noted that when the protected fat was administered that they observed a slight reduction in milk fat percentages and that this depression may be mediated at the mammary gland level. However, they also did not disclose any causal relationship between trans-fatty acid administration and milk fat percentages.
Thus, none of these studies established any causal relationship between trans-fatty acids and low fat levels in cow's milk, and Rindsig et al and Selner et al in fact even taught against any causal role of trans fatty acids in the reduction of fat levels in cow's milk.
The only study known to the inventors which contains any evidence of a causative relationship between the administration of trans-fatty acids and the reduction of milk fat percentages was effected by three of the present inventors. This study was published in the Journal of Nutrition, 1990, (120:818). In this study three of the present co-inventors examined the effects on milk fat percentages in a strain of mice fed a diet containing unsaturated cis-fatty acids, as compared to a diet containing a mixture of cis and trans-fatty acids. The mice which were fed the mixture of cis and trans-fatty acids were found to have reduced milk fat percentages relative to the mice fed only cis-fatty acids. The authors therefore postulated that this decrease was attributable to trans-fatty acids; and that this phenomena may occur in other species, including cows.
However, the experiments reported in this article would, of course, not be viewed as predictive of such a causal relationship in cows given the great dissimilarity of their digestive tracts, most particularly that cows have a ruminant digestive system and mice do not. This difference is particularly noteworthy given the prior recognition in the art that administration of some fatty acids can have adverse effects on the cow's rumen digestive system. In particular, ingestion of free fatty acids may be deleterious to essential digestive microbia contained in the rumen. Accordingly, given the great dissimilarities of a rumen digestive system and a non-rumen digestive system, the experiments conducted by Teter et at. Journal of Nutrition, 1990, (120:818), limited to mice are not regarded to be in any way predictive for ruminants, and specifically cows.
Accordingly, prior to the present invention, there existed a great need in the art for a convenient, safe and relatively inexpensive method for reducing milk fat levels. There further existed a need for identifying those trans-fatty acids which when ingested would reduce fat levels and optionally enhance milk yields so that ruminant diets may be designed for the regulation of milk fat content and optionally milk yields.